Electronic Preprints

There are currently 3 electronic preprints awaiting publication. They are listed below in reverse chronological order.

2025

Title: Superconducting properties of thin film Nb_1−xTi_xN studied via the NMR of implanted ⁸Li
Author: M. Asaduzzaman, R. M. L. McFadden, E. Thoeng, Y. Kalboussi, I. Curci, T. Proslier, S. R. Dunsiger, W. A. MacFarlane, G. D. Morris, R. Li, J. O. Ticknor, R. E. Laxdal, T. Junginger
Abstract: We report measurements of the normal-state and superconducting properties of thin-film Nb_1−xTi_xN using ⁸Li β-detected nuclear magnetic resonance (β-NMR). In these experiments, radioactive ⁸Li⁺ probes were implanted ∼21 nm below the surface of a Nb_1−xTi_xN(91 nm) film in Nb_0.75Ti_0.25N(91 nm)/AlN(4 nm)/Nb and its NMR response recorded (via ⁸Li's β-emissions) between 4.6 K and 270 K in a 4.1 T field applied normal to its surface. Resonance measurements reveal wide, symmetric lineshapes at all temperatures, with significant additional broadening below the film's superconducting transition temperature T_c(0 T) = 15.4 ± 0.7 K due to vortex lattice formation. Fits to a broadening model find a magnetic penetration depth λ(0 K) = 180.57 ± 0.30 nm and upper critical field B_c2(0 K) = 18 ± 4 T, consistent with literature estimates. Spin-lattice relaxation (SLR) measurements find a Korringa response at low temperatures, with dynamic (i.e., thermally activated) contributions dominating above ∼100 K. Below T_c, we observe a small H bel-Slichter coherence peak characterized by a superconducting energy gap Δ(0 K) = 2.60 ± 0.12 meV and modest Dynes-like broadening. Our measurements suggest a gap ratio 2Δ(0 K)/k_BT_c(0 T) = 3.92 ± 0.25, consistent with strong-coupling behavior. Sources for the dynamic high-T relaxation are suggested.
: arXiv:2505.1459 [cond-mat.supr-con]

Title: Lithium-ion dynamics in synthetic quartz studied via the NMR of implanted ⁸Li⁺
Author: W. A. MacFarlane, R. M. L. McFadden, S. Spencer, A. Chatzichristos, J. O. Ticknor, D. L. Cortie, M. H. Dehn, S. R. Dunsiger, D. Fujimoto, Z. H. Jang, V. L. Karner, R. F. Kiefl, G. D. Morris, M. Stachura
Abstract: We report β-detected nuclear magnetic resonance (β-NMR) measurements of implanted ⁸Li⁺ in a synthetic single crystal of α-SiO₂ (quartz). At 6.55 Tesla, the spectrum is comprised of a large amplitude broad resonance and a quadrupolar multiplet that is only revealed by an RF comb excitation. The quadrupole splitting is surprisingly small, increases with temperature, and provides information on the implantation site. Supercell density functional theory calculations show that the small EFG is consistent with an in-channel interstitial site (Wyckoff 3a). The spin-lattice relaxation is unexpectedly fast and strongly temperature dependent with a diffusive peak above 200 K and a second more prominent relaxation peak at lower temperature. Analysis of the diffusive relaxation yields an activation barrier 178(43) meV for the isolated Li⁺, in the range of other measurements and calculations. To account for many of the other features of the data, it is suggested that some of the implanted ions trap an electron forming the neutral Li⁰, which is stable over a narrow range of temperatures.
: arXiv:2503.19204 [cond-mat.mtrl-sci]

2020

Title: Digging into MUD with Python: mudpy, bdata, and bfit
Author: D. Fujimoto
Abstract: Used to store the results of μSR measurements at TRIUMF, the Muon Data (MUD) file format serves as a useful and flexible scheme that is both lightweight and self-describing. The application programming interface (API) for these files is written in C and FORTRAN, languages not known for their ease of use. In contrast, Python is a language which emphasizes rapid prototyping and readability. This work describes three Python 3 packages to interface with MUD files and analyze their contents: mudpy, bdata, and bfit. The first enables easy access to the contents of any MUD file. The latter two are implemented specifically for the implanted-ion β-detected NMR (β-NMR) experiment at TRIUMF. These tools provide both an API and graphical user interface (GUI) to help users extract and fit β-NMR data.
: arXiv:2004.10395 [physics.data-an]